Method of microcellular foam molding

Abstract

A method of microcellular foam molding an article is provided with, in one embodiment, filling a mold with a polyolefin compound; adding a crosslinking agent to the polyolefin compound to form a crosslinked mold; placing the crosslinked mold in a second mold having vent holes; placing the second mold in a pressure vessel; dissolving gas under high pressure to form a supercritical fluid (SCF) in the pressure vessel; effusing the SCF through the vent holes into the crosslinked mold to form a SCF permeated mold; releasing pressure of the pressure vessel to cause the SCF permeated mold to foam; and finishing a foamed article in the second mold.

What is claimed is: 
     
       1. A method of microcellular foam molding an article, comprising the steps of:
 (1) filling a mold with a polyolefin compound; 
 (2) adding a crosslinking agent to the polyolefin compound to form a crosslinked preform; 
 (3) placing the crosslinked preform in a second mold having a plurality of vent holes; 
 (4) placing the second mold in a pressure vessel; 
 (5) dissolving gas under a predetermined pressure to form a supercritical fluid (SCF) in the pressure vessel; 
 (6) effusing the SCF through the vent holes into the crosslinked preform to form a SCF permeated mold; 
 (7) releasing pressure of the pressure vessel to cause the SCF permeated mold to foam; and 
 (8) finishing a foamed article in the second mold. 
 
     
     
       2. The method of  claim 1 , wherein the polyolefin compound is shaped prior to step (1). 
     
     
       3. The method of  claim 1 , wherein the polyolefin compound comprises at least one of ethylene-vinyl acetate (EVA), polyolefin elastomer (POE), low-density polyethylene (LOPE), and polypropylene (PP). 
     
     
       4. The method of  claim 1 , wherein the polyolefin compound comprises polyolefin, crosslinking agent, filler, and chemical additive; and wherein the polyolefin has 100 parts per hundred rubber (phr), the crosslinking agent has less than 1.2 phr, the filler has less than 20 phr, and the chemical additive has less than 5 phr. 
     
     
       5. The method of  claim 3 , wherein the crosslinking agent comprises peroxide; wherein the filler comprises at least one of calcium carbonate, pulvistalci, mica powder, clay, zinc oxide and titanium dioxide; and wherein chemical additive comprises at least one of paraffin, stearic acid, ate complex and calcium salt. 
     
     
       6. The method of  claim 1 , wherein temperature is in the range of 170-180° C. for crosslinking polyolefin compound in the mold. 
     
     
       7. The method of  claim 1 , wherein electron beam irradiation of 20-50 kGy is applied to form crosslinks in the SCF permeated mold. 
     
     
       8. The method of  claim 1 , wherein the predetermined pressure is in 10-50 MPa range for 0.5-8 hours. 
     
     
       9. The method of  claim 1 , wherein in effusing the SCF, a highest temperature is 3° C. lower than a melting temperature of the polyolefin compound, and a lowest temperature is 5° C. higher than a softening temperature of the polyolefin compound. 
     
     
       10. The method of  claim 1 , wherein step (7) of releasing pressure of the pressure vessel takes about 15 to 1,200 seconds to lower pressure of the pressure vessel to room temperature. 
     
     
       11. A method of microcellular foam molding an article, comprising the steps of:
 (a) filling a mold with elastomers; 
 (b) placing the mold in a second mold having a plurality of vent holes; 
 (c) placing the second mold in a pressure vessel; 
 (d) dissolving gas under high pressure to form a supercritical fluid (SCF) in the pressure vessel; 
 (e) effusing the SCF through the vent holes into the mold to form a SCF permeated mold; 
 (f) releasing pressure of the pressure vessel to cause the SCF permeated mold to foam; and 
 (g) finishing a foamed article in the second mold. 
 
     
     
       12. The method of  claim 11 , wherein the elastomers are shaped prior to step (a). 
     
     
       13. The method of  claim 11 , wherein the elastomer is polyurethane (PU) or thermoplastic elastomer (TPE); and wherein the TPE is thermoplastic polyurethane (TPU), thermoplastic polyester elastomer (TPEE), or a combination thereof. 
     
     
       14. The method of  claim 11 , wherein the predetermined pressure is in 10-50 MPa range for 0.5-8 hours. 
     
     
       15. The method of  claim 11 , wherein in effusing the SCF, a highest temperature is 3° C. lower than a melting temperature of the elastomers, and a lowest temperature is 5° C. higher than a softening temperature of the elastomers. 
     
     
       16. The method of  claim 10 , wherein step (f) of releasing pressure of the pressure vessel takes about 15 to 1,200 seconds to lower pressure of the pressure vessel to room temperature.